In recent years, biodegradable polymer materials have been finding a wide variety of applications including medical materials, drug delivery systems, and environmentally compatible materials. In recent years, in addition to those applications, the biodegradable polymer materials have been requested to provide new functions, and hence various studies have been made. In particular, the introduction of a chemically modifiable functional group into a molecule of a polyhydroxyalkanoate typified by polylactic acid has been examined. For example, there has been reported a compound into which a carboxyl group or a vinyl group is introduced. For example, polymalic acid has been known as a polyhydroxyalkanoate having a carboxyl group at a side chain thereof. An α-type represented by the chemical formula (12) and a β-type represented by the chemical formula (13) have been known as polymers of polymalic acid depending on the form of a polymer.

Of those, a polymer obtained by ring-opening polymerization of a benzyl ester of β-malolactone represented by the chemical formula (14) is disclosed in U.S. Pat. No. 4,265,247 (Patent Document 1) as β-type polymalic acid or a copolymer thereof.
(R14: benzyl group.)In addition, a polymer obtained by copolymerization of a six-membered ring diester monomer and a glicolide or lactide as a cyclic diester or a lactone as an intramolecular ring closure reaction ester of ω-hydroxycarboxylic acid represented by the chemical formula (15) is disclosed in Japanese Patent Application Laid-Open No. H02-003415 (Patent Document 2) as a copolymer containing any one of other hydroxyalkanoic acids typified by α-type polymalic acid-glycolic acid copolymer and glycolic acid.
(R15 represents a lower alkyl group such as a methyl group, an ethyl group, an n-propyl group, an isopropyl group, or a t-butyl group, or a benzyl group.)
Macromolecules 2000, 33 (13), 4619-4627 (Non-Patent Document 1) discloses that 7-oxo-4-oxepanonecarboxylate is subjected to ring-opening polymerization to produce a polymer having an ester group at a side chain thereof, and the polymer is further subjected to hydrogenolysis to produce a polymer having a carboxylic acid at a side chain thereof as a polyhydroxyalkanoate having a carboxylic acid at a side chain thereof. Biomacromolecules 2000, 1, 275 (Non-Patent Document 2) discloses a polymer in which a benzyloxycarbonyl group is introduced into a methylene group at position α of a carbonyl group in the main chain of poly(ε-caprolactone), the polymer being obtained by: allowing lithium diisopropylamide to react with poly(ε-caprolactone); and allowing the resultant to react with benzyl chloroformate. Macromolecular Bioscience 2004, 4, 232 (Non-Patent Document 3) discloses a polymer in which a (benzyloxycarbonyl)methyl group is introduced into a methylene group at position a of a carbonyl group in the main chain of polylactic acid, the polymer being obtained by: allowing lithium diisopropylamide to react with polylactic acid; and allowing the resultant to react with benzyl bromoacetate.
Polymeric Materials Science & Engineering 2002, 87, 254 (Non-Patent Document 4) discloses, as a polyhydroxyalkanoate having a vinyl group at a side chain thereof, a polymer obtained by ring-opening polymerization of α-allyl(δ-valerolactone). Similarly, Polymer Preprints 2002, 43 (2), 727 (Non-Patent Document 5) discloses, as a polyhydroxyalkanoate having a vinyl group at a side chain thereof, a polymer obtained by ring-opening polymerization of 3,6-diallyl-1,4-dioxane-2,5-dione as a six-membered ring diester monomer.
There has been reported a polymer having a new function into which a structure providing functional properties for a polyhydroxyalkanoate into which a chemically modifiable functional group is introduced as described above is introduced. International Journal of Biological Macromolecules 25 (1999) 265 (Non-Patent Document 6) discloses the following. A copolymer of α-type malic acid and glycolic acid is obtained by ring-opening polymerization of a cyclic dimer of α-type malic acid and glycolic acid, and the resultant polymer is deprotected to obtain a polyester having a carboxyl group at a side chain thereof. Tripeptide is chemically modified to the carboxyl group at the side chain, and the resultant polymer is evaluated for cell adhesion. At this time, a good result is obtained.
[Patent Document 1] U.S. Pat. No. 4,265,247
[Patent Document 2] Japanese Patent Application Laid-Open No. H02-003415
[Non-Patent Document 1] Macromolecules 2000, 33 (13), 4619-4627
[Non-Patent Document 2] Biomacromolecules 2000, 1, 275
[Non-Patent Document 3] Macromolecular Bioscience 2004, 4, 232
[Non-Patent Document 4] Polymeric Materials Science & Engineering 2002, 87, 254
[Non-Patent Document 5) Polymer Preprints 2002, 43 (2), 727
[Non-Patent Document 6] International Journal of Biological Macromolecules 25 (1999) 265